Rapid-start cathode-ray tubes



1965 HIROSHI YAMAMOTO ETAL 3,214,627

RAPID-START CATHODE-RAY TUBES Filed Feb. 21, 1962 Fig.

United States Patent 3,214,627 RAPID-START CATHODE-RAY TUBES Hiroshi Yamamoto, Hodogaya-kn, Yokohama, and Yukio Taltanashi, Hiratsuka-shi, Japan, assignors to Tokyo Shibaura Electric Co., Ltd, Kawasaki-shi, Japan, a corporation of Japan Filed Feb. 21, 196.2, Ser. No. 174,819 Claims priority, application Japan, Feb. 24, 1961, 36/7,784 2 Claims. ((Il. 313-337) The present invention relates to improved cathode-ray tubes adapted to start rapidly.

Cathode-ray tubes generally have a cathode structure including a cylindrical cup coated with an electron-emitting material and enclosing a heater wire for indirect heating thereof. Such cathode structure having a substantial heat capacity, the tube employing it may start or be set into proper operation only more than ten seconds after it has been turned on. Therefore, with a television receiving set having a cathode-ray tube of such conventional design, the voice only is first reproduced when the set is turned on, the picture being formed only after a considerable time has elapsed. This phenomenon is conspicuous especially with a transistor type receiving set, since the voice is produced substantially at the same time that the set is turned on with the picture noticeably delayed in showing itself.

The present invention is intended to overcome the above deficiency of conventional cathode-ray tubes especially by providing an improved cathode structure adapted to enable the tube to start rapidly.

According to the present invention, there is provided a rapid'start type cathode-ray tube characterized by a cathode structure including two cathode heater elements adapted to be independently energized and deenergized.

The present invention will now be described in detail with reference to the accompanying drawing, which illustrates some embodiments of the invention. In the drawmg:

FIG. 1 is a fragmentary side elevation, partly in section, showing the essential part of the cathode structure of the inventive cathode-ray tube and the connection between the heater elements and base or terminal pins of the tube in an enlarged scale;

FIG. 2 is a schematic showing of one example of the connection between the heater terminal pins of the tube and the voltage source therefor; and

FIG. 3 is a fragmentary side elevation, partly in section, of another example of the connection between the auxiliary heater element and the terminal pins of the tube.

Referring to the drawing, numeral 1 designates a cathode cup in the form of a bottomed metal cylinder having an end face coated with electron-emitting material; numeral 2, an insulating disc or flange fitted around the cathode cup 1; numeral 3, a main coiled heater element of a larger diameter inserted in said cathode cup; and numeral 4, an auxiliary folded-back heater element inserted in the main heater element 3. The two heater elements are each formed of a wire of metal having a high melting point, such as tungsten, and coated with insulating material such as alumina. The main heater element serves to heat the cathode so as to maintain it at a predetermined operating temperature while the auxiliary heater element serves to heat and rapidly raise the temperature of the cathode when the cathode-ray tube is being started. The opposite ends of the main heater element 3 are respectively connected to terminal or base pins 6 and 7 secured to the tube base while the opposite ends of the auxiliary heater element 4 are connected to one of said terminal pins 7 and a further terminal pin 8, respectively.

In starting the cathode-ray tube constructed as described, the main heater element 3 is energized by applicaswitch 11 are operatively connected with each other in a tion thereon of a rated voltage enough to maintain the cathode at its predetermined operating temperature, while the auxiliary heater element 4 is supplied with a sufliciently high voltage to rapidly heat the cathode. It will be appreciated that the cathode is thus rapidly heated under the action of the main and auxiliary heater elements to a desired elevated temperature providing for rapid starting of the tube. Once the tube has been started, the auxiliary heater element is deenergized so that the cathode is maintained at its predetermined operating temperature without any danger of being overheated. Since the auxiliary heater element is disposed within the main heater coil in spaced apart relation with the cathode cup and is held at the same potential as the main heater, the insulator coating on the auxiliary heater may not only be made in an extremely small thickness to reduce its heat capacity but also be heated to any desired elevated temperature without the danger of its puncturing. This is quite an important fact which makes it possible to design the auxiliary heater element as required to heat the cathode rapidly.

In one practical example of cathode-ray tubes made by the inventors, the auxiliary heater element took the form of a folded-back tungsten wire having a current capacity of 150 ma. at 6.3 volts and carrying a thin alumina coating of approximately 0.03-millimeter thickness. The main heater element was formed of a coiled tungsten wire having a rated capacity of ma. at 6.3 volts. After the auxiliary heater was inserted in the main heater coil, 21 thick alumina coating of approximately 0.07 millimeter thickness was deposited around the coil by spraying to give a sufiicient dielectric strength thereto. The heater assembly was then inserted in a cathode cup to form a cathode-ray tube with heater ratings of 75 ma. and 6.3 volts. In starting this cathode-ray tube, an excessive voltage of 12.6 volts is applied to the auxiliary heater element, the rated voltage of 6.3 volts being impressed upon the main heater element. The current flowing through the auxiliary heater amounts to such a high value of the order of two hundred and several ten millimeters, and thus an extremely large heating power is fed to the cathode structure. Moreover, the auxiliary heater element having a limited heat capacity is heated to a very high temperature in quite a short period of time so that the cathode is rapidly heated to start the tube in a time as short as approximately 2 to 3 seconds. Once the tube has been started, the current through the auxiliary heater element is cut Off and the cathode is held at the predetermined operating temperature to mainaint the tube in operation. It will be appreciated that the inventive cathode-ray tube when employed for example in a television set can markedly enhance its value as a merchandise.

FIG. 2 is a schematic wiring diagram for the heater means of the inventive cathode-ray tube. As shown, the terminal pins of the tube connected with the heater elements therein are also connected with a voltage source 9 to obtain respective desired terminal voltages. The circuit of the terminal pin 7, which is connected to both the main and auxiliary heater elements, includes a series-connected switch 10. The circuit of the terminal pin 8, which is connected to the opposite end of the auxiliary heater element, includes a series-connected time-limit switch 11 of suitable construction. The switch 10 and the time-limit suitable manner so that the latter 11 is automatically opened a desired length of time, as for example three seconds, after the main and auxiliary heater elements have both been activated.

Referring next to FIG. 3, which illustrates another example of the auxiliary heater connection in the tube, one end of the auxiliary heater element 4 and the associated terminal pin 8 may be interconnected by way of a heatresponsive switch 12 for example including a bi-metallic element, arranged to interrupt the current flow to the auxiliary heater element in response to the heat transmitted therefrom to the switch. With such arrangement, there is no need for employing any switch outside the tube for the auxiliary heater. Also, the auxiliary heater element may be connected to the terminal pins for the main heater instead of being provided with separate terminal pins for the auxiliary heater itself. This arrangement has an advantage that it enables the cathode-ray tube according to the present invention to be employed in the existing appliances, which have previously employed a conventional cathode-ray tube.

An important advantageous feature of the present invention lies in a heater arrangement for obtaining an extremely increased heating efficiency particularly in connection with the auxiliary heater element. To this end, the auxiliary heater element is inserted in a main heater element in the form of a coil of a larger diameter, as described above. However, where some slight reduction in the heating efficiency owing to some increase in heat capacity is allowable, an auxiliary heater element carrying an insulator coating of substantial thickness may be inserted in the cathode cup in side-by-side relation with the main heater element. In this case, the main heater element may take the form of a coil of limited diameter or a straight folded wire. It will be apparent to those skilled on the art that the auxiliary heater element may be provided with separate terminal pins independently of those for the main heater element and that the auxiliary heater may also be formed into a coil.

What is claimed is:

1. A cathode-ray tube indirect heater cathode assembly for providing rapid start of the tube characterized by a cathode structure including two cathode heater elements adapted to be independently energized and de-energized; a cathode cup adapted to contain both elements; a pair of leads extending from each element beyond the cup; a plurality of terminals in connection with the leads whereat a first source of potential may be applied to one of the elements, and a second source of potential may be applied to the other of the elements; said other of said elements adapted to maintain the cathode at normal oper- 4. ating temperature; said one of the elements being adapted to produce greater quantities of heat than the other element; means for simultaneously applying the first and second sources of potential to energize both elements; and means for disconnecting one source of potential when the cathode-ray tube has started.

2. A cathode-ray tube indirect heater cathode assembly for providing rapid start of the tube characterized by a cathode structure including two cathode heater elements adapted to be independently energized and dcenergized; a cathode cup adapted to contain both elements; a pair of leads extending from each element beyond the cup; a plurality of terminals in connection with the leads whereat a first source of potential may be applied to one of the elements, and a second source of potential may be applied to the other of the elements; said other of said elements adapted to maintain the cathode at normal operating temperature; said one of the elements being adapted to produce greater quantities of heat than the other element; means for simultaneously applying the first and second sources of potential to energize both elements; and thermally operable means responsive to the heat generated by said elements for disconnecting said first source of potential when normal operating temperature is attained.

References Cited by the Examiner UNITED STATES PATENTS 2,460,883 2/49 Hanchett 315104 2,488,948 11/49 Veazie 313--340 2,5 33,493 12/50 Mitchell 250-13 2,753,480 7/56 Batzle 313340 2,870,366 1/59 Vantol 313337 3,087,082 4/63 Osborne 313337 FOREIGN PATENTS 745,329 3/44 Germany. 787,458 12/57 Great Britain.

DAVID J. GALVIN, Primary Examiner.

JAMES D. KALLAM, Examiner. 

1. A CATHODE-RAY TUBE INDIRECT HEATER CATHODE ASSEMBLY FOR PROVIDING RAPID START OF THE TUBE CHARACTERIZED BY A CATHODE STRUCTURE INCLUDING TWO CATHODE HEATER ELEMENTS ADAPTED TO BE INDEPENDENTLY ENERGIZED AND DE-ENERGIZED; A CATHODE CUP ADAPTED TO CONTAIN BOTH ELEMENTS; A PAIR OF LEADS EXTENDING FROM EACH ELEMENT BEYOND THE CUP; A PLURALITY OF TERMINALS IN CONNECTION WITH THE LEADS WHEREAT AT FIRST SOURCE OF POTENTIAL MAY BE APPLIED TO ONE OF THE ELEMENTS, AND A SECOND SOURCE OF POTENTIAL MAY BE APPLIED TO THE OTHER OF THE ELEMENTS; SAID OTHER OF SAID ELEMENTS ADAPTED TO MAINTAIN THE CATHODE AT NORMAL OPERATING TEMPERATURE; SAID ONE OF THE ELEMENTS BEING ADAPTED TO PRODUCE GREATER QUANTITIES OF HEAT THAN THE OTHER ELEMENT; MEANS FOR SIMULTANEOUSLY APPLYING THE FIRST AND SECOND SOURCEDS OF POTENTIAL TO ENERGIZE BOTH ELEMENTS; AND MEANS FOR DISCONNECTING ONE SOURCE OF POTENTIAL WHEN THE CATODE-RAY TUBE HAS STARTED. 